In one well-known type of third generation, fully computerized elevator control system, a plurality of separate computers are utilized as group controllers (to control dispatching of the cars in a group), car controllers for each of the cars (to control operation and motion of each car), and cab controllers for each car (to control doors and interface with the car operating buttons and lights). This type of system is disclosed generally in U.S. Pat. No. 4,363,381 to Bittar and U.S. Pat. No. 4,497,391 to Mendelsohn et al (FIG. 7). In taller buildings, typically over 10 floors, two group controllers may be provided so as to permit operating some of the cars in a low rise group (such as floors 1-8) and the remaining cars in a high rise group (such as floors 9-15); in taller buildings, more groups may be used.
In some of these situations, one of the cars may be provided with capability to operate at all of the floors (such as for freight or service use). It is known to provide a rear door riser comprising hall call buttons and enunciator lanterns in hallways accessible only through rear doors of the elevator cars. It is also known in such systems to provide a separate riser, constituting semi-hidden hall call buttons and floor enunciator lanterns, which may be mounted inconspicuously in an elevator door frame or the like. The car operating in the hoistway with which the extra riser is associated is typically provided with simplex operation capability, so that it can function in the separate riser independently of the rest of the group and the group controller. Should the group controller fail, the elevators could operate in "wild car" mode, which is simply every car stopping at every floor in its hoistway without regard to hall calls or car calls. In the event of power failure, the simplex car in the special riser could typically operate on emergency power (including fireman service). Other examples of separate risers are found in luxury apartment and condominium buildings, as well as hotels, and buildings with rooftop restaurants. A simple example is the rooftop restaurant which opens for business only after the evening downpeak rush hour of an office building; the separate riser in that case would not be used at all during the day while the elevator operating in the shaft with the separate riser would be servicing all office building floors under normal group control. At evening time, that elevator is taken out of the group and would perform only between the lobby (or other entry floor) level and the rooftop restaurant level. The elevator would be operating in simplex mode, with the remainder of its car call button panel disabled.
In such earlier systems operating with two group controllers, it has been known to provide relay connections from one car to both of the groups. A car which is transferrable from one of the groups to another is referred to in the art as a "swing car"; its transfer is referred to as "swinging"; and its operation outside of its normal group is called "swing operation". This permits switching (for example) from having four cars in the low rise group and two cars in the high rise group to having three cars in each group. However, regardless of other configurational characteristics, the provision of the capability to transfer an elevator from one group which has two risers to another group which has a single riser does not provide any capability to use the extra riser in either group. Thus in the case of failure of the normal riser associated with either group controller, the only option would be wild car operation, without any cognizance of hall calls, and without any enunciation of arriving cars.